What kind of feedback?
- Subsonic - causes your woofers to visibly flap. Can be damaging to them. Saps amp power, can cause clipping (kills tweeters). Usually this is caused by a non rigid rack, bouncy floor, and some kind of half-baked suspension in the table itself (magnetic Clearaudios for sure; maybe Tech DAC air too). Solve this by increasing rigidity under the table. You need a more rigid rack and you may need to brace it (e.g. anchor against a wall) and/or place on a stronger part of the floor. The HRS looks pretty rigid, but maybe not as rigid as it could be for the money (cross bracing?) and like all audiophile products in this range, costs a lot for what it gives. Tower height is a liability, so try to keep the rack as short as is functional (e.g. so you’re not crouching down too much to place a record). KAB rumble filter can also stop this, but it’s not 100% sonically transparent. RIGIDITY IS KEY. The worst problem you will ever get with this kind of feedback is a Clearaudio Innovation Compact (magnetic vertical compliance without enough platter mass to keep it from exciting easily) on a CMS Sotto Voce rack (the tallest one). UGH - I have PTSD from this combination.
- Audible bass - can sound similar to a ground loop, except it’s at zero with nothing playing, and rises with playback volume. It can even hit a "runaway" limit at higher playback SPL. VERY bad. For this you need an isolation platform. NOT a semi-rigid constrained layer damping platform, which does jack at these bass frequencies. You need a suspension. Springs are best, but foam and polymers / sorbothane can work OK for simpler cases. Worst case I heard here was VPI "sandwich" plinth (Avenger, Aries) on that same CMS Sotto Voce rack and the VPI 3D arms - absolutely everything was excitable at ~100Hz, especially the very expensive CMS Black Platinum & Diamond shelves (constrained layer damping). However this is a very common problem for "rigid" turntables without the right support underneath. Note that spring suspensions need to be tuned to the weight load, and properly balanced. SOTA tables work so well because the whole system is pre-tuned and self-contained.
- Midrange frequencies - Now you can try "constrained layer damping" and stillpoints and other such audiophile nonsense, because these frequencies are lower energy and much easier to clean up. But again, a good tuned spring suspension will clean this all up in a snap.
Tech DAS is supposedly an Air bearing (I’ve not used them), which probably implies some kind of compliance (suspension). And you have to be careful stacking suspensions (e.g. never stack springs). So like the Clearaudio Magnetic tables, there will be quirks specific to that, and Tech DAS should be able to help hone in on the right solution ingredients.
But really, for a rack - its job #1 is rigidity. As much as you can get. You can figure out the right isolation platform to use atop it later. Avoid tall towers. Wider base is better. Cross bracing is very good. Those cheap VTI / modular racks have NO rigidity; avoid. The HRS you picked looks reasonably rigid, but money might be better spent looking at say the Adona models w/ cross bracing. I also have also seen Rix Rax (sadly out of production) used to great effect for - they are rigid!
If you have a feedback problem, typically it gets exponentially worse with increased SPL. I’m a loud listener, so it comes to a head easily. A lot of the audiophiles here listen at very low to moderate levels, and may avoid the brunt of issues purely through that.
Some of the "scientific" solutions, like Minus-K, look indeed very interesting.
